Development of spectrometric field analytical systems
A multifunctional portable flow analysis instrument was developed. Using a 50 cm long Teflon AF tubing as final reaction and optical measurement conduit, a liquid core waveguide based fluorescence detector that is transversely illuminated by an addressable light emitting diode array, is combined with a chemiluminescence detector and an absorbance detector with a solid state broadband (400-700 nm) source. Several illustrative experiments have been carried out to test the performance of the instrument in different detection modes. A new LED emitting in the mid UV region with reasonable power output (0.5 mW at 100 mA) was fabricated. Using this LED, a compact gated Terbium dipicolinate photoluminescence measurement system capable of detecting 0.4 nM DPA is built. DPA can be used as a selective marker for detecting bacterial spores, notably that of anthrax. The basic principle of using a highly fluorescent europium complex as an extrinsic dye for the detection of proteinaceous aerosols was also demonstrated using this time-gated detector. An autonomous airborne bacterial spore detection unit was developed. Airborne bacterial spore samples were collected effectively using a dry cyclone sampler. The collected particles were then extracted by dodecylamine solution in a heated extractor. The extracted dipicolinic acid was mixed with Terbium (III) solution in a flow injection system and then detected by a gated fluorescence detector. The limit of detection for the system was 1 B. subtilis spore per 3 L air for a sampling duration of 2 hours, which is a great improvement compared to other systems reported. The system was tested at 4 field sites in Lubbock, TX. A low-cost time-gated detection system using a tuning fork to block the intensive excitation pulse and a conventional PMT to collect the luminescence signal was built. This exhibited a limit of detection of 0.12 nM DPA for terbium dipicolinate luminescence measurements. This approach also solved the baseline drop and sensitivity decrease problem encountered when a gated PMT module was used. Such a detection system would be an ideal choice for many applications using lanthanide enhanced time-gated luminescence detection.